Test the error reporting when preparing to perform a backup.

[a-p-]

This adds some limited testing of the error result returned by Backup().

An error result is intentionally triggered by using the same connection for the source and destination.

[coveralls]

Coverage decreased (-5.03%) to 62.274% when pulling 0e686ca on a-p-:test-backup-error into 3fb7a0e on mattn:master.

[coveralls]

Coverage decreased (-5.03%) to 62.274% when pulling 0e686ca on a-p-:test-backup-error into 3fb7a0e on mattn:master.

[a-p-]

The decrease in coverage is unexpected, since this pull request adds additional testing...

Something might be wrong with Coveralls?

For this pull request's build in Coveralls (378), the "ALL" tab near the bottom shows 8 files, instead of 6 for previous recent builds (like build 377). These files are now listed:

• tool/upgrade.go
• sqlite3_test/sqltest.go

Also, the "CHANGED" and "COVERAGE CHANGED" tabs both show 4 affected files, although 3 of them are listed as unchanged...

backup.go's coverage is showing as increased, as expected, however.

[mattn]

Thank you